what is a corey?
what if i decide not to get coreys? do i still need a substrate?

A cory is a corydoras catfish.

A gravle vac is easy to use. Just stci kthe whole thing under water, then place a bucket under the tank. Feed one end of the vac into the bucket, and go across the gravel. It will remove the nasty stuff and keep the gravel there.

You can get a vac for like $6, and it's extremely worthwhile. Corys don't grow too large for a 10 gallon, as long as you don't have too many. Substrate is very good because it harbors the bacteria in your tank that breaks down fish waste.